1. Field of the Invention
This invention relates to a method for recycling an ink sheet and a thermal transfer printer using the same.
2. Description of Related Art
Thermal transfer printers have been used widely, since those printers can be compact and inexpensive and readily obtain high printing quality. In a conventional thermal transfer printer, an ink sheet, as a recording material, is fed between a thermal head and a platen with a printing paper, and thermal elements of the thermal head are selectively driven to transfer the thermoplastic ink onto the printing paper in accordance with printing data sent to the thermal head. However, most of the ink coated on the ink sheet, except a portion transferred to the paper, is thrown away together with a polymer base film of the ink sheet. This leads to high running costs.
To solve such a problem, some recycling apparatuses for an ink sheet have been devised for restoring the portion transferred to the printing paper. A printer equipped with a recoating mechanism restores portions of an ink layer transferred onto the printing paper, as described in SID 85 Digest, pages 143 to 145, "A Color Thermal Transfer Printer with Recording Mechanism," by Nose et al. The recoating mechanism includes a heat-insulated ink tank, an ink roller with a built-in heater and spiral V-shaped grooves, and a rubber coated reverse roller. Thermoplastic ink in the ink tank is melt by the built-in heater in the ink roller. According to rotation of the ink roller, the ink is conveyed onto the reverse roller. thereby being coated by the reverse roller to an endless ink sheet, which is fed between the reverse roller and a back up plate. Then, the recoated ink sheet is used again for printing.
Another printer restores transferred portions of the ink sheet by using magnetic, conductive ink powder. The ink powder is applied by a brush to an ink sheet while a bias voltage is applied between the brush and a back up electrode disposed behind the ink sheet. The ink sheet is charged in proportion to a product of static capacitance of the ink sheet and the bias voltage and attracts the ink powder. However, the ink powder is not attracted to portions at which the ink is remaining, because the conductive ink serves as only a passage of charge and prevents the occurrence of static electric force. As a result, the ink powder is attracted only to portions at which the ink has been transferred, so that the ink layer of the ink sheet is restored to be almost single layer by using such conductive ink powder.
However, the printer with the recoating mechanism cannot print until the solid ink having a large heat capacity is adequately melt at the beginning of the printing. Moreover, in the case when the printer is to be moved, the ink may still be in a fluid state for a while even after power to the printer is off, so that the ink may be spilt in the printer.
In the case of the printer using the ink powder to restore the ink sheet as described above, the ink powder must be conductive, because the ink powder is applied by electrostatic induction only to portions at which the ink has already transferred and the base film is exposed. Accordingly, the ink powder must be mixed with conductive particles, so that such conductive particles reduces saturation of color when used for a color ink. As a result, when color printing is done with the printer using conductive powder, a range of color reproduction becomes narrow.